1. Field of the Invention
The present invention relates to an electrode unit for a prismatic battery including an electrode group formed comprising positive electrode plates, negative electrode plates, and separators, a prismatic battery, and a method of manufacturing an electrode unit for a prismatic battery.
2. Description of the Related Art
In recent years, portable information devices such as a cellular phone, note book-sized personal computer and so on have become widespread. Those devices aim for higher performance, reduced weight, and miniaturization. Accordingly, the secondary battery for use in the power supply of the portable information devices is required to have reduced size and weight and increased energy density.
On the other hand, for external environment such as considerations to rise in gasoline price and global warming, expectations are raised for an electric vehicle. Besides, a so-called hybrid electric vehicle which uses a gasoline engine and an electric motor as a power source is also commercially available.
It is needless to say that the secondary battery is used as a power supply for the electric vehicle and hybrid electric vehicle. In addition, the secondary battery is required to have reduced size and weight, increased energy density and output, longer life, lower cost, improved reliability and so on.
The portable information device, electric vehicle, or hybrid electric vehicle has limited space to house the secondary battery.
On the other hand, the conventional secondary battery often has a cylindrical shape and thus undesirably creates a gap when it is housed in the limited space.
Hence, in place of the cylindrical battery, a prismatic battery has become mainstream. Typical technologies relating to a prismatic battery include, for example, those described in Patent Document 1 and Patent Document 2.
Patent Document 1 describes a technology in which “a positive electrode plate and a negative electrode plate are stacked with a separator interposed therebetween such that their side edge portions on the opposite sides protrude from opposed portions of both the electrode plates so that the protruding portions are made lead portions to reduce the average distance from the entire surfaces of the electrode plates to the current collectors. Thus, the battery internal resistance value is reduced and the utilization rate of the electrode active material is increased to improve the battery output.”
Besides, Patent Document 2 describes a technology in which “electrode plate end portions are provided on the side surfaces of a battery, and the electrode plate tabs are welded to current collecting terminals in a plate shape to realize a ratio of electrode plate width dimension to electrode plate height dimension of 0.22 to 0.67.”
According to Patent Document 2, the distance to the electrode plate end portion can be reduced to improve the current collection efficiency. In the case of employment of this technology in a prismatic alkaline storage battery, an effect capable of reducing the loss of current in high-rate discharge is provided.    [Patent Document 1] Japanese Patent Application Laid-open No. 2001-93508    [Patent Document 2] Japanese Patent Application Laid-open No. 2001-196091